GouSanSi Sorry for the delay in response! I wasn't sure what I should advise because I was not able to understand how the image separation was done using AI on your end.
A simple way I can think of to separate a character image using Photoshop's functions is to create an action for it. For example, as shown in the following video, you can select the area you want to cut using the "Quick selection tool", then perform an action to create mask based on the selection and do minor steps that occur with it:
Here is the action used in the video:
I'm not sure if this is the kind of method you are looking for, but I hope it helps.
